Define Ports/Pins

When creating Pcells, ports/pins are essential units not only to recognize and define where the input/output of the Pcells are but also to offer the connecting information for the powerful auto-routing function in PhotoCAD.

Ports/Pins from existing PCells

When the PCell already contains some existing PCells with some ports, it is convenient to assign the old port to the port of the new PCell.

If generating a PCell by curve points or line

This often happens when we are creating a PCell with points or lines. First we will create an instance which is a waveguide_type and we assign a curve and to the waveguide_type (waveguide_type(curve=curve).with_port(port_name)). Users can see Straight, Bend or Taper for more details.

Here we call the name of the waveguide_type wg. Then the ports will be added by ports += wg.ports since the position and orientation of the port is already defined when generating the instance wg. The names is added when the waveguide_type has the function with_port(name=port_name) being defined.

The ports generated by wg.ports function should be added to the port container, mostly referred to ports.
If the existing PCells are instances

This is mostly the common method when generating a new PCell by some existing lower-level PCells. Here the ports are already defined in the old PCells with name and position.

To assign the old ports to the ports of the new PCells, we can first call the old port from the old PCell your_cell_name["op_0"]. Then use with_name function to assign the old ports to the designated name. So the total script will look like:
```
old_cell_name["old_cell_port_name"].with_name("new_cell_port_name")
```
Now the port information will be transferred to the new PCell.

Manually adding Ports/Pins

Instead of initiating ports/pins from the existing ports of a Pcell(see examples Splitter, Mzm), we can also create ports/pins from fp.Port or fp.Pin, and this allows users to generate ports individually at any places without the restriction of only on the existing Pcells.

This section is a guide to show you how to add ports/pins from fp.Port or fp.Pin function, and we will create a rectangular where one side of the shape is port and another is pin.

Full Script

import math
from typing import Tuple
from gpdk.technology import get_technology, WG
from fnpcell import all as fp


class fpPinPort(fp.PCell):

    height: float = fp.PositiveFloatParam(default=10)
    width: float = fp.PositiveFloatParam(default=50)
    waveguide_type: WG.FWG.C = fp.WaveguideTypeParam(type=WG.FWG.C)
    port_names: fp.IPortOptions = fp.PortOptionsParam(count=2, default=("op_0", "ep_0"))

    def _default_waveguide_type(self):
        return get_technology().WG.FWG.C.WIRE

    def build(self):
        insts, elems, ports = super().build()
        TECH = get_technology()

        rec = fp.el.Rect(height=self.height, width=self.width, center=(0, 0), layer=TECH.LAYER.FWG_CLD)
        elems += rec

        ports += fp.Port(name=self.port_names[0], position=(-self.width/2, 0),
                         waveguide_type=self.waveguide_type.updated(core_layout_width=self.height), orientation=-math.pi)
        ports += fp.Pin(name=self.port_names[1], position=(self.width/2, 0), metal_line_type=TECH.METAL.M1.W10, orientation=0)



        return insts, elems, ports



if __name__ == "__main__":
    from gpdk.util.path import local_output_file

    gds_file = local_output_file(__file__).with_suffix(".gds")
    library = fp.Library()

    TECH = get_technology()
    # =============================================================
    # fmt: off

    library += fpPinPort()

    # fmt: on
    # =============================================================
    fp.export_gds(library, file=gds_file)
    fp.plot(library)

Section Script Description

Importing necessary function packages

To customize the components in gpdk, fnpcell , typing and math need to be imported because modules such as data format, graphics generation, data processing need to be used. Moreover, graphics in the component layout need to be generated on different process layers, so process information(technology, WG) in gpdk needs to be imported:
```
import math
from typing import Tuple
from gpdk.technology import get_technology, WG
from fnpcell import all as fp
```
Define the properties and methods in the Mzm class
1. Define user-definable parameters:
```
height: float = fp.PositiveFloatParam(default=10)
width: float = fp.PositiveFloatParam(default=50)
port_names: fp.IPortOptions = fp.PortOptionsParam(count=2, default=("op_0", "ep_0"))
```
- height and width are the dimension of the rectangular.
- port_names is used to define the number of ports of the component. Secondly, the ports are named, and the default is default=("op_0", "op_1"), the user can set it by himself.
1. Define the build method.
  - Instances, elements and ports are usually used in device cells, i.e. calls to other cell instances, graphics in this cell and device ports.
    
    The three elements in the device are implemented in the PCell definition by calling the build function module in the parent class PCell:
    def build(self): insts, elems, ports = super().build()
  - Generate the rectangular geometry as a element by fp.el.Rect and initiate to the ElementSet(elems).:
    rec = fp.el.Rect(height=self.height, width=self.width, center=(0, 0), layer=TECH.LAYER.FWG_COR) elems += rec
  - Generate the ports/pins by fp.Port/Pin. Note here the name of the ports/pins can be named by the users (type should be str). position can also be adjust by at, e.g. at=component["op_0], to assign a new port to the existing port
    ports += fp.Port(name=self.port_names[0], position=(-self.width/2, 0), waveguide_type=TECH.WG.FWG.C.WIRE.updated(core_layout_width=self.height), orientation=-math.pi) ports += fp.Pin(name=self.port_names[1], position=(self.width/2, 0), metal_line_type=TECH.METAL.M1.W10, orientation=0)
  - Return the instances, elements, and ports in the component cell.
```
return insts, elems, ports
```

View the layout

We can see from the above figure that we have created a rectangular with height=10, width=50. The left port named op_0 is an optical port with a width = 10, and the right port named ep_0 is then an electrical port with also a width = 10. The two ports which we defined individually are able to recognize by the auto-routing function.